Sen. Marco Rubio of Florida, said to be on Mitt Romney's list of possible running mates, said Wednesday the US must exercise strong leadership, for the world's sake. Overall, his eagerly awaited speech on foreign affairs treaded lightly on Obama's policies.

Senate Foreign Relations Committee member Sen. Marco Rubio, R-Fla. speaks about foreign policy, on April 25, at the Brookings Institution in Washington.

Jacquelyn Martin/AP

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Washington — Sen. Marco Rubio of Florida, considered a “short-lister” to share the top Republican ticket with MItt Romney, is adamant about this: Only American leadership can deliver the global freedom and prosperity the 21st century promises.

That was the main message Wednesday from the son of refugees from Fidel Castro’s Cuba, during a speech billed by some in Washington as the Republicans' opening shot in an election-year battle with President Obama over US foreign policy. Their aim: to paint Mr. Obama as timid in standing up to the world’s tyrants and as disregarding the robust American leadership the world needs.

But Senator Rubio did not differ with the Obama administration on much of fundamental importance. He said he would have kept the US at the helm of NATO’s Libya operation longer, would do more to challenge Russia as it attempts a world leadership comeback, and would offer a prescription for Syria that sounds much like what the administration is already doing.

Rubio’s sharpest warning, in fact, was a challenge to those from the left and the right who call for turning inward and who insist that America’s days of global leadership are past. Rubio described this argument as “one that increasingly says it is time to focus less on the world and more on ourselves.”

Rubio referred to Robert Kagan’s book, “The World America Made” (known to be on Obama’s bedside table), and noted that every world order has had its dominant nation. When constituents ask him, "Isn’t it time for someone else to lead the world?," Rubio says his “short answer is … there is no one else to hand off the baton to, even if that were a good idea.”

Expectations were so strong that Rubio would blast Obama for failing to grasp America’s unique role in the world that the Democratic National Committee on Wednesday sent out a “prebuttal” to Rubio’s speech. In its e-mail, the DNC reminded recipients that Obama called the US “the one indispensable nation in world affairs” in his State of the Union address in January.

But Rubio treaded lightly on Obama, saying he agreed with some of the president’s foreign policy moves and not others, perhaps recognizing that voters give Obama relatively high marks on his management of foreign affairs.

In his speech, Rubio said the administration is “correct” that global problems increasingly require international coalitions. But those coalitions, he said, “need to be instigated and led, and more often than not they can only be instigated and led by us.” It's that last point, he added, that “this administration doesn’t understand.”

Rubio cited last summer’s Libya campaign as an example. He insisted that the US should have remained in the lead of the operation longer, instead of handing it over to France and Britain. Doing so, he said, would have expedited the fall of Muammar Qaddafi, cost less because the operation would have been shorter, and spared more of Libya's infrastructure.

But on Syria, Rubio advocated actions that are already part of the Obama administration’s policy, and he pointedly went only so far as to say the US should “potentially” equip the opposition with weapons – thus distancing himself from more hawkish colleagues, including his mentor, Sen. Joseph Lieberman (I) of Connecticut, who had introduced Rubio to the audience. The US first needs to gain a better sense of who the rebels are, Rubio said.

That's an unusually cautious stance for a man known to champion those whom he calls the world's "freedom fighters" – perhaps an indication that Rubio is keeping one eye on the GOP's vice-presidential slot.